1. Field of the Invention
This invention relates to an automatic focus detecting apparatus for detecting the defocus amounts of a plurality of areas of an image field and effecting the focus adjustment of a photo-taking lens.
2. Related Background Art
In the automatic focus detecting apparatus of a camera, there is well known an automatic focus adjusting method whereby light beams from an object passed through different exit pupil areas of a photo-taking lens are imaged on a pair of line sensors and the amount of displacement of the relative positions of a pair of image signals obtained by photoelectrically converting the object image is found to thereby detect the defocus amount of the object and the photo-taking lens is driven on the basis thereof.
There is further a construction in which a plurality of such focus detecting systems are disposed so that focus detection in a plurality of areas can be accomplished, or a construction in which line sensors are disposed cruciformly, whereby whether the distribution of the quantity of light in the same area is in a vertical direction or in a horizontal direction, focus detection is possible.
Where there is a plurality of focus detecting systems, a defocus amount is found for each focus detecting system and thus, a plurality of defocus amounts are detected and therefore, among these defocus amounts, a defocus amount for effecting focus adjustment needs be selected. Heretofore, when selecting the defocus for use for focus adjustment from among the defocus amounts of a plurality of areas, a plurality of results of focus detection obtained in the manner described above have been compared to determine the final defocus amount. However, the focus detecting operations for a plurality of focus detection areas do not terminate at a common time because the accumulation times of sensors are irregular due to the brightness of an object or the like. This has led to a disadvantage that when the accumulation in one of the sensors at respective focus detection points does not terminate, the total focus detecting time becomes long. In order to solve this, there has been proposed a method of effecting focus detection with the accumulation in the sensors being interrupted, but it is often the case that the result of focus detection of the focus detection areas for which the accumulation has been interrupted is not suitable for focus detection and thus, after all, useless focus detection calculation is effected.
Also, in the prior-art method of determining defocus, several conditions have been successively judged and the final defocus amount has been determined. That is, sequential judgement has been done in such a manner that at first, the reliability of the object image is judged from the contrast thereof, and then the degree of coincidence between images is judged with respect to images of good contrast, and finally is judged by the defocus amount to determine the final focus detection area.
In such a method, however, there is the possibility of selecting a focus detection area unsuitable for focus detection depending on the order in which judgement is done or the condition under which judgement is done, and correct focus detection is hampered.